[107.05D] Probing the innermost regions of luminous and ultra-luminous infrared galaxies: Sensitive VLBI continuum and HI absorption observations of the ULIRG IRAS17208-0014 and the LIRG NGC7674.

E. Momjian (U. of Kentucky/NRAO)

Very long baseline interferometry (VLBI) is one of the few
techniques capable of revealing the highly obscured
innermost regions of luminous and ultra-luminous infrared
galaxies (LIRGs & ULIRGs) in the nearby universe.
Observations at 21 cm show the uniqueness of VLBI
measurements in revealing the details of the structure and
the kinematics in the nuclear regions of these galaxies.
Here, we present sensitive VLBI results on two galaxies, the
ULIRG IRAS 17208-0014 and the LIRG NGC 7674.

The high resolution continuum images of IRAS 17208--0014 at
1.36 GHz reveal the details of the nuclear starburst region
of this galaxy. Both diffuse and compact continuum emission
are detected. The compact sources are more likely clustered
luminous radio supernovae and supernova remnants. The
results suggest a massive star formation rate of ~84
M\odot~{\rm yr}-1 and a supernova rate of ~4 {\rm
yr}-1. A very wide HI absorption line is associated with
this galaxy. This line is composed of several components
with velocity widths between 58 and 232 km/s, and column
densities on the order of 1020~T\rm s(K).

The image of NGC 7674 at 1.38 GHz and 20 mas resolution
reveals previously undetected continuum structures in the
nuclear region of this galaxy. At 11 \times 5 mas
resolution, three compact sources can be seen in the central
region with brightness temperatures ~108 K. One of
these sources is a possible candidate to host an AGN.
Several HI absorption features with optical depths \leq
0.4 are seen toward both compact and extended continuum
sources.

The National Radio Astronomy Observatory is a facility of
the National Science Foundation operated under cooperative
agreement by Associated Universities, Inc.